There are a number of prior art devices and methods used for plasma etching of semiconductor wafers. One successful such apparatus and method is disclosed and depicted in U.S. Pat. No. 4,464,223, for which a Reexamination Certificate was issued on Apr. 9, 1991. This plasma etch reactor depicts a reactor chamber which is bounded by three electrodes. An upper electrode is grounded, while a lower electrode is provided with a low frequency power supply along with a DC power supply. The lower electrode is also the chuck which holds the semiconductor wafer in position. Another electrode is located between the upper and lower electrodes and is positioned about the periphery of the reactor chamber in substantially cylindrical in shape. This electrode is provided with a high radio frequency power supply. In this arrangement, the high and low frequency power supplies are used to optimize (1) the disassociation of the process gases, and (2) the ion energy of the plasma generated reactant species.
While the above device has been very successful in operation, it has been found that more precise control of the plasma within the reactor chamber would be beneficial to the operation of a plasma etch reactor.